This invention relates to a magnetic medium, such as a thin film magnetic recording medium, and the method of manufacturing the medium. The invention has particular applicability to high density magnetic recording media having a total film thickness above a substrate of about 1000 xc3x85 or less while still exhibiting low noise, improved flying stability, glide performance and head-media interface reliability.
Magnetic disks and disk drives are conventionally employed for storing data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducing heads positioned in close proximity to the recording surfaces of the disks and moved generally radially with respect thereto. Magnetic disks are usually housed in a magnetic disk unit in a stationary state with a magnetic head having a specific load elastically in contact with and pressed against the surface of the disk.
Data are written onto and read from a rapidly rotating recording disk by means of a magnetic head transducer assembly that flies closely over the surface of the disk. It is considered desirable during reading and recording operations to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. This objective becomes particularly significant as the areal recording density increases. The areal density (Mbits/in2) is the recording density per unit area and is equal to the track density (TPI) in terms of tracks per inch times the linear density (BPI) in terms of bits per inch.
The increasing demands for higher areal recording density impose increasingly greater demands on flying the head lower because the output voltage of a disk drive (or the readback signal of a reader head in disk drive) is proportional to 1/exp(HMS), where HMS is the space between the head and the media. Therefore, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk to be positioned in closer proximity with an attendant increase in predictability and consistent behavior of the air bearing supporting the head.
A substrate material conventionally employed in producing magnetic recording rigid disks comprises an aluminum-magnesium (Alxe2x80x94Mg) alloy. Such Alxe2x80x94Mg alloys are typically electrolessly plated with a pre-coat layer of NiP at a thickness of about 15 microns to increase the hardness of the substrates, thereby providing a suitable surface for polishing to provide the requisite surface roughness or texture.
Other substrate materials have been employed, such as aluminum, glass, e.g., an amorphous glass, glass-ceramic material which comprise a mixture of amorphous and crystalline materials, and ceramic materials. Glass-ceramic materials do not normally exhibit a crystalline surface. Glasses and glass-ceramics generally exhibit high resistance to shocks. The use of glass-based materials, such as glass-ceramic materials, is disclosed by Hoover et al., U.S. Pat. No. 5,273,834, which is incorporated herein by reference.
A conventional longitudinal recording disk medium is depicted in FIG. 1. It typically comprises a substrate 10, comprising an aluminum platter with a 10-15 microns thick NiP pre-coat layer, and sequentially deposited on each side of the substrate are an underlayer 11, 11xe2x80x2, such as chromium (Cr) or Cr-alloy, a magnetic layer 12, 12xe2x80x2, typically comprising a cobalt (Co)-base alloy, and a protective overcoat 13, 13xe2x80x2, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer 11, 11xe2x80x2, magnetic layer 12, 12xe2x80x2, and protective overcoat 13, 13xe2x80x2, are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer. A conventional perpendicular recording disk medium is similar to the longitudinal recording medium depicted in FIG. 1, but does not comprise Cr-containing underlayers.
Conventional methods for manufacturing longitudinal magnetic recording medium comprise applying a seed layer between the substrate and underlayer. A seed layer seeds the nucleation of a particular crystallographic texture of the underlayer.
Longitudinal magnetic recording media with substrates having an Al, Alxe2x80x94Mg, glass or glass-ceramic support are commercially available from different manufacturers with a pre-coat layer of materials that influence the crystallographic orientation of subsequently deposited seed layer and/or underlayer and magnetic layers. Pre-coat on the support of the substrate also facilitates laser texturing and mechanical texturing process. Such conventional pre-coat layer materials include nickel-phosphorous (Nixe2x80x94P) which is typically sputter deposited on the surface of the bare substrate.
Conventional longitudinal magnetic recording media comprising a substrate having NiP sputtered thereon also comprise, sequentially deposited thereon, a Cr or Cr-alloy seed layer and/or underlayer at an appropriate thickness, e.g., about 750 xc3x85, a magnetic layer such as Coxe2x80x94Cr-platinum (Pt)-tantalum (Ta) at an appropriate thickness, e.g., 250 xc3x85, and a protective carbon overcoat at an appropriate thickness, e.g., about 75 xc3x85. Conventional Cr-alloy seed layer and/or underlayer comprise vanadium (V), titanium (Ti), tungsten (W) or molybdenum (Mo). Other conventional magnetic layers are CoCrTa, CoCrPtB, CoCrPt, CoCrPtTaNb and CoNiCr. The seed layer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the glass or glass-ceramic substrate in an inert gas environment, such as an environment of pure argon. A conventional carbon overcoat is typically deposited in argon with nitrogen, hydrogen or ethylene plasma. Conventional lubricant topcoats are typically about 20 xc3x85 thick. In short, in conventional recording media the thickness of all of the layers deposited on the substrate having a NiP pre-coat layer is typically more than 1000 xc3x85. When the thickness of all the layers above the NiP pre-coat layer is about 1000 xc3x85 or more, migration of Ni to the top surface of the recording was not recognized to be a problem.
However it has been observed that Ni ion migration onto the top surface of the recording media becomes more severe as the total film thickness of the media decreases. Ni atoms can diffuse to the top of overcoat and form micro-crystal clusters, which make recording head more vulnerable and cause disk drive failure. Applicants found that Ni from the NiP layer leaches from the substrate to the top surface of the medium while also promoting leaching of Co from the magnetic layer to the top surface of the medium when the thickness of all layers on top of the NiP pre-coat layer is 1000 xc3x85 or less, particularly about 500 xc3x85 or less. Applicants also found that corrosion products on the top surface are picked up by a low-flying recording head of a high density medium causing smearing on the recording head and disc surface, resulting in increased stiction and eventual drive failure. Therefore, applicants recognized that there is a need to find sealing layers, which enhance magnetic recording performances, reduce Ni migration, and have good adhesion to the substrates. This invention provides a method to prevent Ni migration onto the top surface of the media during the manufacturing process and the life of the recording media.
The present invention is a magnetic recording medium comprising a substrate containing Ni that does not significantly migrate to the surface of the recording medium. In one embodiment, the substrate comprises a support and a Ni-containing pre-coat layer on the support.
Another advantage of the present invention is a method of manufacturing a magnetic recording medium comprising a substrate containing Ni that does not significantly migrate to the surface of the medium.
Additional advantages and other features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a magnetic recording medium comprising longitudinal or perpendicular magnetic recording medium comprising a substrate comprising Ni, a sealing layer comprising metal oxide, and a magnetic layer, wherein the sealing layer substantially prevents the migration of Ni from the substrate.
Another embodiment of this invention is a longitudinal or perpendicular magnetic recording medium comprising a substrate comprising Ni, a sealing means for substantially preventing the migration of Ni from the substrate, and a magnetic layer. Embodiments of the sealing means include a sputter deposited layer of a sealing material such as metal oxide, preferably amorphous metal oxide, most preferably amorphous CrOx, that substantially prevents the migration of Ni from the substrate in which the support may be an Al-containing support, e.g., Al or Alxe2x80x94Mg, or made of glass or glass-ceramic materials. In this invention, CrOx refers to an oxide of Cr. Similarly, TiOx, MoOx, WOx, TaOx, ZrOx and NbOx refer to an oxide of Ti, an oxide of Mo, an oxide of W, an oxide of Ta, an oxide of Zr and an oxide of Nb, respectively.
The sealing layer or the sealing means can substantially prevent the migration of Ni from the substrate by limiting nickel ions migrating onto a top surface of the medium to an intensity of 1012 atoms/cm2 or less during the lifetime of the recording medium when the thickness of the layers above the substrate starting from the sealing layer is 1000 xc3x85 or less. In a preferred embodiment, the thickness of the layers above the substrate starting from the sealing layer is 750 xc3x85 or less. In a more preferred embodiment, the thickness of the layers above the substrate starting from the sealing layer is 500 xc3x85 or less.
Another aspect of the present invention is a method comprising sputter depositing sealing layer comprising metal oxide, preferably amorphous CrOx, on substrate comprising Ni and sputter depositing a magnetic layer on the sealing layer, wherein the sealing layer substantially prevents migration of Ni from the substrate.
Embodiments include sputter depositing a Cr layer on a nickel-containing layer and then oxidizing the Cr layer by exposure to argon and oxygen premixed gas to form the CrOx sealing layer, which optionally comprises boron (B), tungsten (W), tantalum (Ta), Zirconium (Zr), Niobium (Nb) and phosphorus (P).
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. The drawings and description are to be regarded as illustrative in nature, and not as restrictive.